Derby Talk

Derby Talk is a forum for Pinewood Derby, Awana Grand Prix, Kub Kar Rally, Shape N Race Derby, Space Derby, Raingutter Regatta and other similar races where a child and an adult work together to create a race vehicle and a lot of fun and memories

IMO, aero isn't the first, or even the second prime factor in a fast car.

Friction is. And the 2 things that affect friction the most are alignment and axle/wheel bore prep. Without these, no car will be fast. But a car without a great aero shape or weight placement can still be fast if the friction is minimalized.

Now, the point of the post is "before you cut that block". So I guess aero is a major consideration before you do that, no doubt.

Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.

Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.

We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.

Our "before you cut that block" emphasis is related to alignment (friction), not aerodynamics. We make sure that the kids press their axle holes before they cut the block, so all the sides of the block are still square.

We saw a huge improvement in the overall performance of the cars in our derby when we started having the kids press their axle holes with a drill press at our workshops. But aerodynamics doesn't make that much of a difference.

Sure, the cars that add a lot of (low-density) material to make the car significantly bigger (e.g., my Calvin & Hobbes car, my sub sandwich car, my friend's banana split car) are slow. But the race winners might be low-profile "Hershey bar" designs, or they might be typical "cut the original block into a car shape" designs.

We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.

Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.

We don't to the drill/press holes until after the block is cut and weight pockets routed, etc. Basically until all the wood working is done, in case the work warps it. And they WILL warp. So we drill the axle holes (whether using the slots or not) last.

Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.

I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.

Same here. one of the last things I do. It can be tricky making sure you don't temporarily warp the car in drill setup and then it will look like you can't drill straight when you check the drill job. i think this is going off topic, but being that the intent of the thread was mislead by the title... it may of already been off topic.

For the beginner it might be better to drill the block first under the assumption the block is square to start with. which i haven't found one that has been in my last 8 years of doing it.

I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.

Ah, clever, I like the idea of making the barely-touching wheel more slippery! Finally a reason for graphite on the tread!

I don't worry about whether the block is square or not. Doesn't matter, because the drill fixture is going to drill perfectly parallel holes regardless. And since the fronts are going to be steering, doesn't matter if they're straight that much, either. Even for a 4 wheel touching car (the single most idiotic rule in PWD), still going to make it a rail runner. Just make one wheel *barely* touch, then lube the tread up with graphite so if it does touch it doesn't "grip". And then steer it with the other.

Ah, clever, I like the idea of making the barely-touching wheel more slippery! Finally a reason for graphite on the tread!

Yep, we make 'em look like those graphite-coated wheels you can buy, lol